Multi-level sensing circuit and semiconductor memory device including the same

ABSTRACT

A multi-level sensing circuit for a multi-level memory device configured to “recognize” more than two different voltages. The multi-level voltage sensing circuit may include a pre-charge controller configured to pre-charge a pair of bit lines with a bit-line pre-charge voltage level in response to an equalizing signal during a sensing mode. The multi-level voltage sensing circuit may include a read controller configured to maintain a voltage of the pair of bit lines at the bit-line pre-charge voltage level in response to a read control signal during a sensing operation. The multi-level voltage sensing circuit may include a sense-amplifier configured to generate data of the pair of bit lines during the sensing mode. The multi-level voltage sensing circuit may include a voltage sensor configured to generate the equalizing signal by comparing a bit-line voltage with a reference voltage.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority filing date of Korean patentapplication No. 10-2018-0012930, which was filed on Feb. 1, 2018. Thedisclosure of that application is hereby incorporated in its entirety byreference.

BACKGROUND 1. Technical Field

Embodiments of the present disclosure may generally relate to amulti-level sensing circuit and a semiconductor device including thesame, and more particularly to a technology for sensing multiple levels(multi-level).

2. Related Art

Dynamic Random Access Memory or “DRAM” is a well-known semiconductormemory device. It is also known as a “volatile” memory device.

A DRAM memory cell comprises a cell transistor and a cell capacitor. Thecell transistor controls access to the cell capacitor. The DRAM cellcapacitor stores electric charge. The state of that charge correspondsto binary-valued data. Stated another way, stored data in a prior artDRAM is classified as either high-level or low-level data depending onthe amount of an electric charge stored in the DRAM cell capacitor. Whena word line of a DRAM semiconductor device is enabled, charge-sharingoccurs between a bit line and a bit line bar, i.e., the Boolean logiccomplement of the value on the bit line. A sense-amplifier then operatesto determine the state of the charge on the DRAM capacitor.

In addition to a cell transistor and capacitor, a DRAM also includes adriver and/or a sense-amplifier, which transmit signals through a lineor a bus. A DRAM memory cell also typically includes a sense-amplifier,which outputs data generated from a plurality of memory cells, to a datatransfer line or data bus.

Semiconductor devices, including memory devices, continued to decreasein size. There is, however, a limit on how small a semiconductor,including semiconductor memory devices, can be made.

Prior art memory devices store data using only two different values orlevels If data can be stored in a memory device that is capable of usingmore than two values or levels, more data can be stored per unit areathan can be stored in a two-valued memory device.

SUMMARY

Circuitry disclosed herein senses multiple different voltage levels thatrepresent different data values or different information and convertsthose different voltage levels to binary valued voltage that correspondto binary-valued data.

In one embodiment, a multi-voltage level sensing circuit includes apre-charge controller, which pre-charges “bit lines” with a bit-linepre-charge voltage in response to an equalizing signal during a sensingmode. The multi-level sensing circuit also includes a read controller,which maintains a voltage of the bit lines at the bit-line pre-chargevoltage level in response to a read control signal during a sensingoperation. A sense-amplifier generates data from the bit lines duringthe sensing operation and, a voltage sensor generates an equalizingsignal by comparing a bit-line voltage with a reference voltage.

In accordance with another embodiment of the present disclosure, asemiconductor device includes: a sense-amplifier configured to include afirst pull-down power line and a second pull-down power line, and sensedata of a pair of bit lines in response to drive voltages applied tofirst and second pull-down power lines during a sensing operation; avoltage controller configured to selectively supply bias voltages havingdifferent levels to the first and second pull-down power lines inresponse to drive signals activated at different times during thesensing operation; and a data converter configured to compare firstsensed data and second sensed data received from the pair of bit lineswith each other, and discriminate data in response to inversion ornon-inversion of the compared data.

In accordance with another embodiment of the present disclosure, amulti-level sensing circuit includes: a first sense-amplifier configuredto receive a drive voltage through a second pull-down power line and afourth pull-down power line; a second sense-amplifier configured toreceive a drive voltage through a first pull-down power line and a thirdpull-down power line; a first voltage controller configured to supplybias voltages having different levels to the first and second pull-downpower lines in response to first and second drive signals during asensing mode; and a second voltage controller configured to supply biasvoltages having different levels to the third and fourth pull-down powerlines in response to the first drive signal and a third drive signalduring the sensing mode.

Those of ordinary skill in the art should understand that the foregoingSummary and the following Detailed Description are for purposes ofillustration. The true scope of the subject matter claimed is set forthin the claims.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic diagram of a first embodiment of a semiconductormemory device that includes a first embodiment of a multi-level sensingcircuitry.

FIG. 2 is a schematic diagram of the first embodiment of a multi-levelsensing circuit shown in FIG. 1.

FIG. 3 is a timing diagram illustrating the operation of the multi-levelsensing circuit shown in FIG. 2.

FIG. 4 is a schematic diagram of second embodiment of a semiconductormemory device that includes a second embodiment of a multi-level sensingcircuitry

FIG. 5 is a schematic diagram of the second embodiment of a multi-levelsensing circuit used in the circuit shown in FIG. 4.

FIG. 6 is a timing diagram illustrating operations of the multi-levelsensing circuit that is shown in FIG. 5.

FIG. 7 is a schematic diagram of a third embodiment of a semiconductormemory device that includes a third embodiment of a multi-level sensingcircuit; the present disclosure.

FIG. 8 is a schematic diagram of the third embodiment of a multi-levelsensing circuit used in the circuit shown in FIG. 7.

DETAILED DESCRIPTION

As used herein, relational terms such as first and second, top andbottom, and the like are used solely to distinguish one entity or actionfrom another entity or action without necessarily requiring or implyingany actual such relationship or order between such entities or actions.The terms “comprises,” “comprising,” or any other variation thereof, areintended to cover a non-exclusive inclusion, such that a process,method, article, or apparatus that comprises a list of elements does notinclude only those elements but can include other elements not expresslylisted or inherent to such process, method, article, or apparatus. Anelement proceeded by “comprises . . . a” does not, without moreconstraints, preclude the existence of additional identical elements inthe process, method, article, or apparatus that comprises the element.And, like reference numbers are used to identify the same or similarstructures in the different embodiments and views.

As used herein and for claim construction purposes, the term“multi-level” should be construed to mean more than two, i.e., three ormore. In a conventional, binary-valued or digital logic circuit, a logiczero and a logic one are represented by two different voltages, themagnitudes and polarities of which are a design choice. A multi-levelsensing circuit is thus a circuit that can sense, detect or identifythree or more distinctly different voltages and produce an output signalrepresentative of each. For some embodiments, a multi-level sensingcircuit may be a multi-level voltage sensing circuit. For someembodiments, a multi-level memory device may include at least one cellarray including at least one memory unit cell. For some embodiments, asemiconductor memory device may be a multi-level semiconductor memorydevice. For some embodiments, a memory device may include at least onecell array including at least one memory unit cell.

FIG. 1 is a schematic diagram of a first embodiment of a semiconductormemory device 10. It comprises a cell array 100, a multi-level sensingcircuit 200, and a data converter 300. As shown in the figure, themulti-level sensing circuit 200 actually comprises two separatemulti-level sensing circuits, the details of which are shown in FIG. 2,

The cell array 100 comprises two or more memory unit cells MC1 and MC2.As shown in the figure, memory unit cell MC1 comprises a singleswitching element T1, embodied in FIG. 1 as a field-effect transistor(FET) and a single capacitor C1. The capacitor stores voltages ascharges, the value or magnitude of which represents data. Differentvoltages or charges stored on the capacitor C1 can representcorrespondingly different scalar information. By way of example, threedifferent voltages on C1 can be representative of integers zero, one andtwo.

Those of ordinary skill in the art will recognized that the “drain”terminal of FET switching element T1 is coupled to a “bit line,” BL. Thecapacitor C1, is coupled between the “source” terminal of FET switchingelement T1 and a ground or other reference potential. C1 can thus becharged or discharged using signals on the bit line, BL, and the wordline, WL.

Still referring to FIG. 1, the memory unit cell MC2 is identical to thememory unit cell MC1 but of course comprises a separate FET switchingelement denominated as “T2” and a separate capacitor denominated as“C2.”

A first multi-level sensing circuit 200 shown in FIG. 1 comprises twoseparate multi-level sensing circuits 210 and 220, which sense thecharge that represents “data” stored in the cell array 100. The sensingcircuit 210 is able to pre-charge the bit line BL in response to a writecontrol signal WVBLP, which occurs during a write operation. During aread operation, the sensing circuit 210 reads or obtains “data” from thememory unit cell MC1 and outputs a sense signal CD1, responsive to aread control signal RVBLP and reference voltages VREF1 and VREF2. Asecond sensing circuit 220 is identical to the first sensing circuit200.

The data converter 300 converts the multi-valued sensing signals CD1 andCD2 received from the multi-level sensing circuit 200 to binary-valuedoutput data identified in FIG. 1 as BIT 1, BIT 2 and BIT 3. Logic levelsof the sensing signals CD1 and CD2 applied to the data converter 300 areshown in the following Table 1.

TABLE 1 CD1 CD2 0 0 0 1 1 0 1 1 0 VBLP VBLP 0 1 VBLP VBLP 1

Logic levels of the 3-bit data BIT1˜BIT3 output from the data converter300 may be established as shown in the following Table 2.

TABLE 2 BIT1 BIT2 BIT3 0 0 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1

The sensing signals CD1 and CD2 detected by the multi-level sensingcircuit 200 can be more than two values, e.g., either data “0”, data“1”, or a bit-line pre-charge voltage (VBLP) level. The bit-linepre-charge voltage (VBLP) level can be set to ½×VCC (i.e., a half levelof a power-supply voltage VCC). The data converter 300 decodes thesensing signals CD1 and CD2, and thus outputs 3, binary-digit, i.e.,3-bit data values denominated as BIT1, BIT2 and BIT3, which are ofcourse either a logic 1 or logic 0.

FIG. 2 is a schematic diagram of the first embodiment of a multi-levelsensing circuit shown in FIG. 1. Since the sensing circuits 210 and 220shown in FIG. 1 are identical, a detailed description of only the firstsensing circuit 210 is provided.

Referring now to FIG. 2, the sensing circuit 210 comprises a pre-chargecontroller 211, a read controller 212, a sense-amplifier 213, and apre-charge voltage sensor 214.

Upon receiving a bit-line equalizing signal BLEQ, an equalizing signalEQ, and a write control signal WVBLP, the pre-charge controller 211 maypre-charge a pair of bit lines (BL, BLB) with a bit-line pre-chargevoltage (VBLP) level.

The pre-charge controller 211 comprises three NMOS FET transistors(N1˜N3) and an OR gate, OR1. The gate terminals of the NMOS transistors(N1˜N3) receive an output signal of the OR gate OR1, which controls ordetermines when those transistors are on and off. A first transistor N1is coupled between two separate bit lines, BL and BLB. The other,series-connected transistors, N2 and N3, are coupled between the bitlines BL and BLB and receive a pre-charge voltage (VBLP) level throughtheir common connection node.

Those of ordinary skill in the art should recognize that when the outputof OR gate OR1 goes “high” transistors N1-N3 turn on. The transistorsN1-N3 thus turn on when any one or more of the bit-line equalizingsignal BLEQ, the equalizing signal EQ, and the write control signalWVBLP, are high or active.

The read controller 212 comprises series-connected transistors N4 and N5coupled across the BL and BLB lines. A read control signal, RVBLP, whichis provided to the gate terminals of N4 and N5, controls when thosetransistors are turned on. When the read control signal RVBLP is active,as happens during a sensing operation, the read controller 212 allowsthe bit lines BL and BLB to be maintained at a common, pre-chargevoltage level, VBLP that is provided to both N4 and N5. The readcontroller 212 can thus adjust current flowing in the bit lines (BL,BLB) responsive to the read control signal RVBLP during a sensingoperation. The read control signal RVBLP is enabled by synchronizing itwith activation of the sense-amplifier 213 during the sensing operation.In an embodiment, the read controller 212 may include a plurality ofNMOS transistors N4 and N5 and a resistor R. In an embodiment, each ofthe NMOS transistors N4 and N5 may be implemented as a transistor havinga longer channel length as compared to each transistor included in thesense-amplifier 213. In an embodiment, each of the NMOS transistors N4and N5 may be implemented as a transistor having a longer channel lengthas compared to each transistor included in the pre-charge controller211.

The NMOS transistors N4 and N5 may be coupled in series between the bitlines (BL, BLB), such that the NMOS transistors N4 and N5 may receivethe read control signal RVBLP through a common gate terminal thereof.The resistor R may be coupled between a bit-line precharge voltage(VBLP) input terminal and a common node of the NMOS transistors N4 andN5.

Still referring to FIG. 2, the sense-amplifier 213 comprises NMOStransistors N6 and N7 and PMOS transistors P1 and P2. A common sourceterminal for the PMOS transistors P1 and P2 is coupled to a pull-uppower line LA. A common source terminal for the NMOS transistors N6 andN7 is coupled to a pull-down power line LAB. A common gate terminal ofthe PMOS transistor P1 and the NMOS transistor N6 is coupled to the bitline BL. A common gate terminal of the PMOS transistor P2 and the NMOStransistor N7 is coupled to the bit line bar BLB.

The sense amplifier 213 is essentially a latch and is thus consideredherein as providing a memory cell. During a sensing operation, thesense-amplifier 213 latches data on the bit lines BL, BLB). Asemiconductor memory device, such as a dynamic random access memory(DRAM), may include the sense-amplifier 213.

After accessing each memory cell in the sense-amplifier 213, chargesharing is achieved between the memory cell and the pair of bit lines(BL, BLB) in the sense-amplifier 213. As a result, the sense-amplifier213 essentially amplifies differences between the bit lines BL and BLB.

A pre-charge voltage sensor 214 comprises two voltage comparators, A1and A2, the outputs of which are provided to a conventional OR gate,OR2. The pre-charge voltage sensor compares the voltage on bit line BLto each of two reference voltages VREF1 and VREF2. The output of thepre-charge voltage sensor, EQ, goes active when the voltage on bit lineBL is greater than either or both of the reference voltages. Thereference voltage VREF1 and the reference voltage VREF2 may be differentvoltages. Reference voltage VREF1 may be greater than reference voltageVREF2. For example, the reference voltage VREF1 may be set to a levelgreater than ½×VCC (i.e., a half level of the power-supply voltage VCC);reference voltage VREF2 may be set to a level less than ½×VCC.

The combination circuit 215 may output the equalizing signal EQ bycombining output signals of the comparators A1 and A2. In this case, thecombination circuit 215 may include an OR gate OR2. When at least one ofthe output signals of the comparators A1 and A2 is activated, thecombination circuit 215 may activate and output the equalizing signalEQ.

The multi-level sensing circuit 200 shown in FIG. 2 will hereinafter bedescribed with reference to the timing diagram of FIG. 3, which is atiming diagram illustrating operation of the multi-level sensing circuit210 shown in FIG. 1.

Referring now to both FIG. 2 and FIG. 3, when the equalizing signal BLEQ(See FIG. 2.) provided to OR gate OR1 is active during a pre-chargeoperation, bit lines (BL, BLB) are-pre-charged through N2 and N3 withthe bit-line pre-charge voltage (VBLP). When the write control signalWVBLP (See FIG. 2.) is subsequently activated during a write operation,(See WL in FIG. 3.) the NMOS transistors N1˜N3 of the pre-chargecontroller 211 are turned on again. Thereafter, data received on the bitlines (BL, BLB), embodied as voltage levels differing from the VBLPvoltage level, are latched or stored in the sense amplifier 213 (SeeLA/LAB in FIG. 3.) and thus stored in the cell array 100 shown inFIG. 1. When the equalizing signal BLEQ (See FIG. 2.) is activated againduring a pre-charge mode, the bit lines (BL, BLB) are “re-pre-charged”with the bit-line pre-charge voltage (VBLP) level. Previously-writtendata can thus be removed from BL and BLB.

Subsequently, when a row address strobe (RAS) signal acting as a mainsignal for operating the DRAM device is activated, so that an address isinput to a row address buffer (not shown). In this case, a row decodingoperation for selecting one of word lines WL contained in the cell array100 is carried out by decoding the row address signals.

Data of cells coupled to a selected word line WL is applied to the pairof bit lines (BL, BLB). As a result, a sense-amplifier (also called asense-amp) enable signal indicating an operation start time of thesense-amplifier 213 is enabled to drive a sense-amp driving circuit of acell block selected by the row address signals. Stated another way, whenthe bit-line equalizing signal BLEQ is de-activated and the word line WLis activated during a read operation, the sense-amplifier 213 operates(i.e., time period T1). During operation of the sense-amplifier 213, adrive voltage is input to the pull-up power line LA and the pull-downpower line LAB (i.e., time period T2). If the sense-amplifier 213 startsoperation, voltages of the bit lines (BL, BLB) that have even a smallpotential difference between them are “transitioned” or changed orconverted to instead have a high potential difference between them.

When the read control signal RVBLP transitions to a high level at T2,the sensing circuit 210 shown in FIG. 2, outputs the sensing signal CD1shown in FIG. 1, by detecting data on the bit lines (BL, BLB). When adata value equal to a logic “1” is stored in the unit cell MC1, thesensing circuit 210 senses a level of the data “1” that is higher thanthe reference voltage VREF1 through the bit line BL. Thus, the sensingsignal CD1 is output as the data value logic “1”. When a data valueequal to logic “0” is stored in the unit cell MC1, the sensing circuit210 senses a voltage level of the logic “0” that is lower than thereference voltage VREF2 through the bit line bar BLB. Thus, the sensingsignal CD1 may be output as the data “0”.

When data having a level denoted by (½×VCC) is stored in the unit cellMC1, the pre-charge voltage sensor 214 activates the equalizing signalEQ by detecting a voltage level of the bit line BL. For example, whenthe voltage of the bit line BL is less than the reference voltage VREF1and is higher than the reference voltage VREF2, the pre-charge voltagesensor 214 may activate the equalizing signal EQ.

When the equalizing signal EQ (See FIG. 2.) is activated, the bit lines(BL, BLB) are pre-charged with the bit-line pre-charge voltage (VBLP)level by the pre-charge controller 211 during a sensing operation.Between T2 and T6, during which time the read control signal RVBLP isactive, NMOS transistors N4 and N5 of the read controller 212 are turnedon. The VBLP voltage is applied to both bit lines (BL, BLB), which arethus maintained at the bit-line pre-charge voltage (VBLP) level duringthe sensing operation. The bit-line pre-charge voltage VBLP is slowlyapplied to the pair of bit lines (BL, BLB) through the resistor R, suchthat the bit lines (BL, BLB) remain unchanged at the (½×VCC) level. Thatis, the pre-charge controller 211 according to the embodiment mayoperate in the pre-charge mode, and may perform the pre-charge operationby the equalizing signal EQ in the sensing mode, such that the pair ofbit lines (BL, BLB) can sense the bit-line pre-charge voltage (VBLP)level.

At T6, (See FIG. 3.) the bit-line equalizing signal BLEQ isre-activated. The read control signal RVBLP (See FIG. 2.) is alsodeactivated. The bit lines (BL, BLB) are thus pre-charged again to theVBLP voltage level or “re pre-charged.” The multi-level sensing circuits210 and 220 can thus read data “1” and data “0” but also read the(½×VCC) level (bit-line pre-charge voltage level), thereby sensingmultiple voltage levels, each of which correspond to a different datavalue. The pre-charge controller 211, read controller 212, senseamplifier 213 and voltage sensor 214 that comprise the multi-levelsensing circuits 210, 220 are thus considered to be circuits orstructures, which are each “configured” to effectuate the sensing, aswell as the storage of multiple different voltages, each level of whichcan be associated with a corresponding different data value.

FIG. 4 is a schematic diagram of second embodiment of a semiconductormemory device 40, which includes a second embodiment of a multi-levelsensing circuitry. The semiconductor device 40 comprises a cell array100_1, a multi-level sensing circuit 400, and a data converter 500. Thecell array 100_1 of FIG. 4 is identical in structure to the cell array100 of FIG. 1. A description of the cell array 100_1 in FIG. 4 istherefore omitted in the interest of brevity.

The multi-level sensing circuit 400 in FIG. 4 comprises two sensingcircuits 410 and 420, which are configured to sense data stored in thecell array 100_1. The sensing circuit 410 reads data of the unit cellMC1 in the cell array 100_1 in response to a read control signal RVBLPduring a data read operation and outputs sensing signal CD1. Likewise,sensing circuit 420 reads data of the unit cell MC2 in response to theread control signal RVBLP during the data read operation and outputs thesensing signal CD2.

The multi-level sensing circuit 400 of FIG. 4 periodically sensesvoltage levels detected by the cell array 100_1 several times (e.g.,twice) at predetermined time intervals. The multi-level sensing circuit400 performs a mismatching of a voltage applied to a latch stage of asense-amplifier, instead of comparing the voltage level detected by thecell array 100_1 with the reference voltage, such that the multi-levelsensing circuit 400 discriminates or differentiates different voltagelevels corresponding to data, generated during a data sense operation.The multi-level sensing circuit 400 is better understood by reference toFIG. 5.

The data converter 500 in FIG. 4, converts sensing signals CD1 and CD2received from the multi-level sensing circuit 400 to output data signalsidentified in FIG. 4 as BIT, 1, BIT 2 and BITS. Operations of the dataconverter 500 for outputting the 3-bit data (BIT1˜BITS) is identical tothe of the data converter 300 of FIG. and as such a detailed descriptionthereof will herein be omitted in the interest of brevity. In FIG. 4,however, the sensing signal CD1 can be input to the data converter 500periodically, i.e., at predetermined time intervals. The data converter500 in FIG. 4 can thus discriminate data by comparing a former sensingsignal CD1 with a latter sensing signal CD2. The data converter 500 maythus include a latch circuit 510 to store the former sensing signal CD1therein.

FIG. 5 is a detailed circuit diagram illustrating the multi-levelsensing circuit 400 shown in FIG. 4. Since the sensing circuit 410 andthe other sensing circuit 420 for use in the multi-level sensing circuit400 are identical in structure to each other, a detailed description ofonly the sensing circuit 410 shown in FIG. 5 will hereinafter bedescribed for illustrative purpose and better understanding of thepresent disclosure.

The sensing circuit 410 comprises a pre-charge controller 411, asense-amplifier 412, a voltage controller 413, a drive signal generator414, and a voltage generator 415. Those of ordinary skill in the artshould recognize that the pre-charge controller 411 pre-charges bitlines (BL, BLB) with a pre-charge voltage (VBLP) in response to thebit-line equalizing signal BLEQ during the pre-charge mode.

The precharge controller 411 may include a plurality of NMOS transistorsN8˜N10. The NMOS transistors (N8˜N10) may receive the bit-lineequalizing signal BLEQ through a common gate terminal thereof. The NMOStransistor N8 may be coupled between the bit lines BL and BLB. The NMOStransistors N9 and N10 may be coupled in series between the bit lines(BL, BLB), and may receive the precharge voltage (VBLP) level through acommon connection node thereof.

Just as its name suggests, the sense-amplifier 412 senses data on thebit lines (BL, BLB) during a data sense operation. The sense-amplifier412 comprises NMOS transistors N11 and N12 and PMOS transistors P3 andP4 coupled as shown in the figure.

The PMOS transistors P3 and P4 are coupled to a pull-up power line, RTO,through a common source terminal. The PMOS transistors P3 and P4 arecross-coupled to each other through their respective gate terminals.

NMOS transistor N11 is coupled between the PMOS transistor P3 andpull-down power line SB1. The gate terminal of the NMOS transistor N11is coupled to the bit line BL.

NMOS transistor N12 is coupled between PMOS transistor P4 and pull-downpower line SB2. The gate terminal of NMOS transistor N12 is coupled tobit line bar, BLB.

The output of inverter IV1 provides the sensing signal CD1, by invertingthe signal at the node between PMOS transistor P3 and the NMOStransistor N11.

The voltage controller 413 comprises NMOS transistors N13˜N16. Itselectively provides either a bias voltage VBIAS0 or VBIAS1 to thepull-down power lines SB1 and SB2 in response to a drive signal, eitherSAN1 or SAN2, during a sense operation.

NMOS transistor N13 is coupled between the pull-down power line SB1 andthe bias voltage VBIAS0. VBIAS0 is applied to SB1 when NMOS transistorN13 receives drive signal SAN1.

NMOS transistor N14 is coupled between pull-down power line SB2 and biasvoltage VBIAS1. VBIAS 1 is applied to SB2 when NMOS transistor N14receives drive signal SAN1.

NMOS transistor N15 is coupled between the pull-down power line SB1 andthe other bias voltage VBIAS1. VBIAS1 is thus applied to SB1 when NMOStransistor N15 receives drive signal SAN2.

Similarly, NMOS transistor N16 is coupled between pull-down power lineSB2 and bias voltage VBIAS0. VBIAS0 is thus provided to SB2 when NMOStransistor N16 receives the drive signal SAN2.

The sense-amplifier 412 shares the pull-down voltages SB1 and SB2 withsense-amplifiers SA formed in a contiguous region.

The voltage controller 413 may be included in a sub-hole region. In thiscase, the sub-hole region may represent an intersection region of thesense-amplifier 412 and a word-line drive circuit. For example, thesub-hole region may include a sub-wordline drive circuit, asense-amplifier (sense-amp) driver for generating a sense-amplifierdrive signal, a bit-line equalizing driver for generating a bit-lineequalizing signal BLEQ, and a bit-line isolation driver for generating abit-line isolation signal, etc.

The drive signal generator 414 provides the bias voltages, SAN1 and SAN2in response to a read control signal, RVBLP. The drive signal generator414 periodically activate the bias voltages SAN1 and SAN2 at intervalshaving predetermined times during activation of the read control signalRVBLP.

The voltage generator 415 can generate bias voltages VBIAS0 and VBIAS1having different voltage levels. For example, the bias voltage VBIAS0may be greater than VBIAS1. The bias voltage VBIAS0 may also be lessthan ½×VCC. The bias voltage VBIAS1 may also have a value identical toor greater than the ground voltage (VSS) level or other referencepotential.

FIG. 6 is a timing diagram illustrating operations of the multi-levelsensing circuit 400 shown in FIG. 5. Referring now to both FIG. 5 andFIG. 6, when the equalizing signal BLEQ (See FIG. 5.) is activatedduring a pre-charge operation, the bit lines BL, BLB are pre-chargedwith the bit-line pre-charge voltage, VBLP. When the bit-line equalizingsignal BLEQ is subsequently deactivated, and the word line WL (See FIG.6.) is activated during a read operation, the sense-amplifier 412 startsoperation, at which time, voltages are applied to the pull-up power lineRTO of the sense amplifier 412 and to the pull-down lines SB1 and SB2.

When the read control signal RVBLP (See FIG. 5.) is activated to a highlevel, the drive signal generator 414 periodically activates the drivesignals SAN1 and SAN2 for selectively supplying the bias voltages VBIAS0and VBIAS1 to the pull-down power lines SB1 and SB2 of thesense-amplifier 412 at intervals of a predetermined time. The drivesignal SAN1 may be activated earlier than the drive signal SAN2.

When the drive signal SAN1 is activated, the NMOS transistors N13 andN14 are turned on, which applies bias voltage VBIAS0 to the pull-downline SB1 and bias voltage VBIAS1 to the pull-down line SB2. Thesense-amplifier can then sense data of the bit line BL, and output thesensing signal CD1.

Thereafter, when the drive signal SAN2 is activated, the NMOStransistors N15 and N16 are turned on. Bias voltage VBIAS1 is applied topull-down power line SB1 and bias voltage VBIAS0 is applied to pull-downline SB2. The sense-amplifier 412 can then sense data of the bit lineBL, and output the sensing signal CD1.

The embodiment shown in FIG. 5 can supply the same voltage (bit-linepre-charge voltage VBLP) to the pair of bit lines (BL, BLB) and mayadjust the bias voltages VBIAS0 and VBIAS1 applied to the pull-downpower lines SB1 and SB2 of the sense-amplifier 412, and thusdiscriminate data. That is, threshold voltages of the pull-down powerlines SB1 and SB2 are adjusted in different ways such that a voltageapplied to the latch stage is intentionally mismatched and a data levelcan be sensed.

For example, the voltage applied to the pull-down power line SB1 duringeach of the first and second sensing operations may be output as avoltage level denoted by a solid line of FIG. 6. In contrast, thevoltage applied to the pull-down power line SB2 during each of the firstand second sensing operations may be output as a voltage level denotedby a dotted line of FIG. 6.

The data converter 500 senses multiple levels (multi-level) bydiscriminating the sensing signal CD1 generated from the sensing circuit410. That is, during a first sensing operation, the data converter 500can store the sensing signal CD1 received from the sensing circuit 410in the latch circuit 510. During the second sensing operation, the dataconverter 500 may compare the sensing signal CD1 received from thesensing circuit 410 with the signal stored in the latch circuit 510,thereby discriminating data.

For example, when each of a first sensing signal and a second sensingsignal is output as data “1”(high level), the data converter 500 maydetermine data to be “1”. When each of the first sensing signal and thesecond sensing signal is output as data “0”(low level), the dataconverter 500 may determine the data to be “0”.

When the first sensing signal and the second sensing signal aredifferent from each other as shown in the timing diagram of FIG. 6, thedata converter 500 may determine the (½×VCC) level. Referring to thetiming diagram of FIG. 6, the voltage applied to the pull-down powerline SB1 during the first sensing operation and the voltage applied tothe pull-down power line SB1 during the second sensing operation mayhave different voltage levels. Likewise, the voltage applied to thepull-down power line SB2 during the first sensing operation and thevoltage applied to the pull-down power line SB2 during the secondsensing operation may have different voltage levels.

That is, when data “1” is detected during the first sensing operationand data “0” is detected during the second sensing operation, the dataconverter 500 may determine the sensing data to be the (½×VCC) level. Incontrast, when data “0” is detected during the first sensing operationand data “1” is detected during the second sensing operation, the dataconverter 500 may determine the sensing data to be the (½×VCC) level.

FIG. 7 is a circuit diagram illustrating a representation of an exampleof a semiconductor device 70 according to still another embodiment ofthe present disclosure. In FIG. 7, the semiconductor device includes thesame cell array 100_1 described above. It also includes a multi-levelsensing circuit 600 and a data converter 700.

The multi-level sensing circuit 600 comprises two identical sensingcircuits 610 and 620, which sense data stored in the cell array 100_1.During a read operation, the sensing circuit 610 reads data of the unitcell MC1 in response to the read control signal RVBLP. It outputssensing signals CD3 and CD4. Likewise, during a read operation, thesensing circuit 620 reads data of the unit cell MC2 in response to theread control signal RVBLP and outputs sensing signals CD5 and CD6.

The multi-level sensing circuit 600 of FIG. 7 discriminates differentvoltage levels on BL and BLB by mismatching a voltage applied to thelatch stage of the sense-amplifier. It controls two sense-amplifiers tosimultaneously sense voltages of latch stages. It controls the levelsrespectively detected by the bit lines BL and BLB to be different fromeach other by mismatching bias voltage levels applied to latch stages oftwo sense-amplifiers, thereby detecting multiple levels (multi-level).Operations of the multi-level sensing circuit 600 shown in FIG. 7 willhereinafter be described with reference to FIG. 8.

The data converter 700 in FIG. 8 converts the signals CD3, CD4, CD5 andCD6 received from the multi-level sensing circuit 600 to binary outputdata signals identified in FIG. 7 as BIT1, BIT 2 and BITS. Operations ofthe data converter 700 for outputting data BIT1˜BIT3 by decoding thesensing signals CD3˜CD6 are identical to those of the data converter 300of FIG. 1, and as such a detailed description thereof will herein beomitted for convenience of description.

However, the sensing circuit 610 according to the embodiment of FIG. 7may simultaneously detect two sensing signals CD3 and CD4 received fromtwo latch stages, such that the sensing circuit 610 may compare the twosensing signals CD3 and CD4 with each other, thereby discriminating adata level.

FIG. 8 is a detailed circuit diagram illustrating a representation of anexample of the multi-level sensing circuit 600 shown in FIG. 7. Sincethe sensing circuit 610 and the other sensing circuit 620 for use in themulti-level sensing circuit 600 are identical in structure to eachother, a detailed description of only the sensing circuit 610 shown inFIG. 8 will hereinafter be described for illustrative purpose and betterunderstanding of the present disclosure.

Referring to FIG. 8, the sensing circuit 610 may include a plurality ofsense-amplifier groups SA_G1˜SA_G3, voltage controllers 614 and 615, avoltage generator 616, and a drive signal generator 617.

In this case, since the sense-amplifier groups SA_G1˜SA_G3 are identicalin structure to each other, a detailed description of only thesense-amplifier group SA_G1 shown in FIG. 8 will hereinafter bedescribed for illustrative purpose and better understanding of thepresent disclosure. The sense-amplifier group SA_G1 may include a firstsense-amplifier 611, a second sense-amplifier 612, and a controller 613.A detailed circuit of the first sense-amplifier 611 is identical instructure to that of the second sense-amplifier 612, and as such adetailed description thereof will herein be omitted for convenience ofdescription.

In this case, the first sense-amplifier 611 may receive a drive voltagefrom the voltage controller 614 through the pull-down power line SB2,and may receive a drive voltage from the voltage controller 615 throughthe pull-down power line SB4. The first sense-amplifier 611 may outputthe sensing signal CD3 detected through the sensing node SA_F.

The second sense-amplifier 612 may receive a drive voltage from thevoltage controller 614 through the pull-down power line SB1, and mayreceive a drive voltage from the voltage controller 615 through thepull-down power line SB3. The second sense-amplifier 612 may output thesensing signal CD4 detected through the sensing node SA_S.

The controller 613 may selectively control the first sense-amplifier 611and the second sense-amplifier 612 in response to a sensing enablesignal SEN. For example, the controller 613 may control the firstsense-amplifier 611 and the second sense-amplifier 612 to simultaneouslyoperate in the sensing section in which the sensing enable signal SEN isactivated, such that the sensing signals CD3 and CD4 detected throughthe sensing nodes SA_F and SA_S can be simultaneously output. Incontrast, the controller 613 may stop operation of the firstsense-amplifier 611 and the second sense-amplifier 612 in a deactivationsection of the sensing enable signal SEN, such that the sensing signalsCD3 and CD4 are not output.

The voltage controller 614 may supply the bias voltage VBIAS1 or theground voltage VSS to the pull-down power lines SB1 and SB2 during thesensing mode. The voltage controller 614 may include a plurality of NMOStransistors N17˜N20.

The NMOS transistor N17 may be coupled between the pull-down power lineSB1 and the ground voltage (VSS) input terminal, such that the NMOStransistor N17 may receive the drive signal SAN1 through a gate terminalthereof. The NMOS transistor N18 may be coupled between the pull-downpower line SB2 and the bias voltage (VBIAS1) input terminal, such thatthe NMOS transistor N18 may receive the drive signal SAN1 through a gateterminal thereof. The NMOS transistor N19 may be coupled between thepull-down power line SB1 and the bias voltage (VBIAS1) input terminal,such that the NMOS transistor N19 may receive the drive signal SANthrough a gate terminal thereof. The NMOS transistor N20 may be coupledbetween the pull-down power line SB2 and the ground voltage (VSS) inputterminal, such that the NMOS transistor N20 may receive the drive signalSAN through a gate terminal thereof.

The voltage controller 615 may supply the bias voltage VBIAS2 or theground voltage VSS to the pull-down power lines SB3 and SB4 during thesensing mode. The voltage controller 615 may include a plurality of NMOStransistors N21˜N24.

In this case, the NMOS transistor N21 may be coupled between thepull-down power line SB3 and the bias voltage (VBIAS2) input terminal,such that the NMOS transistor N21 may receive the drive signal SAN2through a gate terminal thereof. The NMOS transistor N22 may be coupledbetween the pull-down power line SB4 and the ground voltage (VSS) inputterminal, such that the NMOS transistor N22 may receive the drive signalSAN2 through a gate terminal thereof. The NMOS transistor N23 may becoupled between the pull-down power line SB3 and the ground voltage(VSS) input terminal, such that the NMOS transistor N23 may receive thedrive signal SAN through a gate terminal thereof. The NMOS transistorN24 may be coupled between the pull-down power line SB4 and the biasvoltage (VBIAS2) input terminal, such that the NMOS transistor N24 mayreceive the drive signal SAN through a gate terminal thereof.

In accordance with the embodiment of the present disclosure, therespective sense-amplifiers of the plurality of sense-amplifier groupsSA_G1˜SA_G3 may share the pull-down power lines SB1˜SB4 with oneanother.

The voltage generator 616 may generate bias voltages VBIAS1 and VBIAS2having different voltage levels. For example, the bias voltage VBIAS1may be higher in level than the bias voltage VBIAS2. The bias voltageVBIAS1 may be lower in level than the (½×VCC) level. The bias voltageVBIAS2 may be identical in level to or higher than the ground voltage(VSS) level.

The drive signal generator 617 may generate the drive signals SAN, SAN1,and SAN2 in response to the read control signal RVBLP. In other words,the drive signal generator 617 may activate the drive signals SAN, SAN1,and SAN2 during activation of the read control signal RVBLP.

Operations of the sensing circuit 610 shown in FIG. 8 will hereinafterbe described with reference to the attached drawings.

When the word line WL is activated during the read mode, thesense-amplifier group SA_G1 may operate. During operation of the firstsense-amplifier 611 and the second sense-amplifier 612, the drivevoltage may be applied to the pull-down power lines SB1˜SB4.

When the read control signal RVBLP is activated to a high level, thedrive signal generator 617 may activate the drive signals SAN, SAN1, andSAN2 for selectively supplying the bias voltages VBIAS1 and VBIAS2 orthe ground voltage VSS of the pull-down power lines SB1˜SB4 of the firstsense-amplifier 611 and the second sense-amplifier 612. In this case,the drive signals SAN, SAN1, and SAN2 may be simultaneously activated.

When the drive signal SAN is activated, the NMOS transistors N19, N20,N23, and N24 are turned on. Accordingly, the bias voltage VBIAS1 may beapplied to the pull-down power line SB1, and the ground voltage VSS maybe applied to the pull-down power line SB2, The ground voltage VSS maybe applied to the pull-down power line SB3, and the bias voltage VBIAS2may be applied to the pull-down power line SB4.

When the drive signals SAN1 and SAN2 are activated, the NMOS transistorsN17, N18, N21, and N22 are turned on. Thus, the ground voltage VSS maybe applied to the pull-down power line SB1, and the bias voltage VBIAS1may be applied to the pull-down power line SB2. The bias voltage VBIAS2may be applied to the pull-down power line SB3, and the ground voltageVSS may be applied to the pull-down power line SB4. Accordingly, thesensing signals CD3 and CD4 detected through the sensing nodes SA_F andSA_S of the first sense-amplifier 611 and the second sense-amplifier 612may be output.

The data converter 700 may detect or sense multiple levels (multi-level)by discriminating the sensing signals CD3 and CD4 generated from thesensing circuit 610. For example, when each of two sensing signals CD3and CD4 is detected as a logic level of data “1”, the data converter 700may discriminate data “1”. When each of two sensing signals CD3 and CD4are detected as a logic level of data “0”, the data converter 700 maydiscriminate data “0”. When the data converter 700 detects or senses thetwo sensing signals CD3 and CD4 having opposite logic levels, the dataconverter 700 may discriminate the (½×VCC) level.

As is apparent from the above description, the multi-level sensingcircuit and the semiconductor device including the same according to theembodiments of the present disclosure can detect and store multi-leveldata in the same cell and thereby store more data per unit area of asilicon die than is possible with prior art binary-only memory devices.

Those skilled in the art will appreciate that the embodiments may becarried out in other specific ways than those set forth herein withoutdeparting from the spirit and essential characteristics of thedisclosure. By way of example, those of ordinary skill will recognizethat the capacitance C1 can be implemented using a single capacitor aswell as two or more capacitors coupled in parallel or series. Similarly,a single transistor can be replaced by multiple transistors; PMOStransistor devices can be substitutes for NMOS transistor devices. Theembodiments described above are therefore to be construed asillustrative and not restrictive. The scope of the disclosure should bedetermined by the appended claims and their legal equivalents, not bythe above description. Further, all changes coming within the meaningand equivalency range of the appended claims are intended to be embracedtherein. In addition, it is obvious to those skilled in the art thatclaims that are not explicitly cited in each other in the appendedclaims may be presented in combination as an embodiment or included as anew claim by a subsequent amendment after the application is filed.

Although a number of illustrative embodiments have been described, itshould be understood that numerous other modifications and embodimentscan be devised by those skilled in the art that will fall within thespirit and scope of the principles of this disclosure. Particularly,numerous variations and modifications are possible in the componentparts and/or arrangements which are within the scope of the disclosure,the drawings and the accompanying claims. In addition to variations andmodifications in the component parts and/or arrangements, alternativeuses will also be apparent to those skilled in the art.

What is claimed is:
 1. A multi-level sensing circuit comprising: apre-charge controller configured to pre-charge a pair of bit lines witha bit-line pre-charge voltage level in response to an equalizing signalduring a sensing mode; a read controller configured to maintain avoltage of the pair of bit lines at the bit-line pre-charge voltagelevel in response to a read control signal during a sensing operation; asense-amplifier configured to generate data of the pair of bit linesduring the sensing mode; and a voltage sensor configured to generate theequalizing signal by comparing a bit-line voltage with a referencevoltage.
 2. The multi-level sensing circuit according to claim 1,wherein the pre-charge controller is configured to pre-charge the pairof bit lines when at least one of a bit-line equalizing signal activatedin a pre-charge mode, a write control signal activated in a write mode,and the equalizing signal is activated.
 3. The multi-level sensingcircuit according to claim 1, wherein the read controller comprises:first and second transistors coupled in series between the pair of bitlines so as to receive the read control signal through a common gateterminal thereof; and a resistor coupled between an input terminal ofthe bit-line pre-charge voltage and a common node of the first andsecond transistors.
 4. The multi-level sensing circuit according toclaim 3, wherein the pre-charge controller has transistors coupledbetween the pair of bit lines, wherein the sense-amplifier hastransistors coupled between the pair of bit lines, and wherein the firstand second transistors include a longer channel length as compared tothe transistors coupled between the pair of bit lines included in thepre-charge controller and the sense-amplifier.
 5. The multi-levelsensing circuit according to claim 1, wherein the pre-charge voltagesensor includes: a first comparator configured to compare the bit-linevoltage with a first reference voltage; a second comparator configuredto compare the bit-line voltage with a second reference voltage having adifferent level from the first reference voltage; and a combinationcircuit configured to output the equalizing signal by combining anoutput signal of the first comparator with an output signal of thesecond comparator.
 6. The multi-level sensing circuit according to claim5, wherein: the first reference voltage is set to a level higher thanthe bit-line pre-charge voltage; and the second reference voltage is setto a level lower than the bit-line pre-charge voltage.
 7. Asemiconductor device comprising: a sense-amplifier configured to includea first pull-down power line and a second pull-down power line, andsense data of a pair of bit lines in response to drive voltages appliedto first and second pull-down power lines during a sensing operation; avoltage controller configured to selectively supply bias voltages havingdifferent levels to the first and second pull-down power lines inresponse to drive signals activated at different times during thesensing operation; and a data converter configured to compare firstsensed data and second sensed data received from the pair of bit lineswith each other, and discriminate data in response to inversion ornon-inversion of the compared data.
 8. The semiconductor deviceaccording to claim 7, wherein the sense-amplifier comprises: third andfourth transistors coupled to a pull-up powerline through a commonsource terminal thereof, such that gate terminals thereof arecross-coupled to each other; a fifth transistor coupled between thethird transistor and a first pull-down power line such that a gateterminal thereof is coupled to a bit line; and a sixth transistorcoupled between the fourth transistor and a second pull-down power linesuch that a gate terminal thereof is coupled to a bit line bar.
 9. Thesemiconductor device according to claim 8, wherein the pair of bit linesare configured to receive a bit-line pre-charge voltage level, prior tothe receipt of information-bearing voltages capable of having more thantwo different values.
 10. The semiconductor device according to claim 7,further comprising: a voltage generator configured to output a firstbias voltage and a second bias voltage having different voltage levelsto the voltage controller.
 11. The semiconductor device according toclaim 10, wherein: the first bias voltage is higher in level than thesecond bias voltage; the first bias voltage is lower in level than abit-line pre-charge voltage; and the second bias voltage is set to alevel that is equal to or higher than a ground voltage level.
 12. Thesemiconductor device according to claim 10, further comprising: a drivesignal generator configured to supply a first drive signal and a seconddrive signal activated at different times to the voltage controller. 13.The semiconductor device according to claim 10, wherein the voltagecontroller includes: a seventh transistor coupled between the firstpull-down power line and a first bias voltage input terminal, andcontrolled by a first drive signal; an eighth transistor coupled betweenthe second pull-down power line and a second bias voltage inputterminal, and controlled by the first drive signal; a ninth transistorcoupled between the first pull-down power line and the second biasvoltage input terminal, and controlled by a second drive signal; and atenth transistor coupled between the second pull-down power line and thefirst bias voltage input terminal, and controlled by the second drivesignal,
 14. The semiconductor device according to claim 7, wherein thevoltage controller is included in a sub-hole region.
 15. Thesemiconductor device according to claim 7, wherein the sense-amplifiershares the first and second pull-down voltage lines with anothersense-amplifier.
 16. The semiconductor device according to claim 7,wherein: the data converter discriminates data “1” when each of a firstsensing signal and a second sensing signal is output as data “1”, anddiscriminates data “0” when each of the first sensing signal and thesecond sensing signal is output as data “0”; and the data converterdiscriminates a bit-line pre-charge voltage level when the first sensingsignal and the second sensing signal are changed.
 17. A multi-levelsensing circuit comprising: a first sense-amplifier configured toreceive a drive voltage through a second pull-down power line and afourth pull-down power line; a second sense-amplifier configured toreceive a drive voltage through a first pull-down power line and a thirdpull-down power line; a first voltage controller configured to supplybias voltages having different levels to the first and second pull-downpower lines in response to first and second drive signals during asensing mode; and a second voltage controller configured to supply biasvoltages having different levels to the third and fourth pull-down powerlines in response to the first drive signal and a third drive signalduring the sensing mode.
 18. The multi-level sensing circuit accordingto claim 17, further comprising: a controller configured to activate thefirst sense-amplifier and the second sense-amplifier during anactivation section of a sensing enable signal.
 19. The multi-levelsensing circuit according to claim 17, wherein the first voltagecontroller includes: an eleventh transistor coupled between the firstpull-down power line and a ground voltage input terminal, and controlledby the second drive signal; a twelfth transistor coupled between thesecond pull-down power line and a first bias voltage input terminal, andcontrolled by the second drive signal; a thirteenth transistor coupledbetween the first pull-down power line and the first bias voltage inputterminal, and controlled by the first drive signal; and a fourteenthtransistor coupled between the second pull-down power line and theground voltage input terminal, and controlled by the first drive signal.20. The multi-level sensing circuit according to claim 17, wherein thesecond voltage controller includes: a fifteenth transistor coupledbetween the third pull-down power line and a second bias voltage inputterminal, and controlled by the third drive signal; a sixteenthtransistor coupled between the fourth pull-down power line and a groundvoltage input terminal, and controlled by the third drive signal; aseventeenth transistor coupled between the third pull-down power lineand the ground voltage input terminal, and controlled by the first drivesignal; and an eighteenth transistor coupled between the fourthpull-down power line and the second bias voltage input terminal, andcontrolled by the first drive signal.